In industrial practice in the case of widely used manipulators, e.g. industrial robots, it is necessary in certain manipulating processes for them to perform mutually coordinated, i.e. synchronous movements or the like. This is e.g. the case if two robots are used for joining and a third robot for welding the joined articles. For this purpose it is necessary in known industrial robots to at least temporarily synchronize regularly present programmable control units, so that at least during certain critical phases a clearly defined, relative movement sequence is ensured.
For this purpose the control programs of known cooperating manipulators contain specific synchronization instructions, which are translated by the interpreter programs transmitting the control program in specific machine instructions and there are then specific method sequences for synchronizing the corresponding manipulators.
In known methods inputs and outputs of robot control units are used for synchronization between the robots. A communication can take place both by means of field bus systems and by means of directly wired inputs and outputs of the control units. This specifically means that the control program for a manipulator contains one or more synchronization instructions and then by means of the operated communication hardware corresponding synchronization signals are transmitted directly to the inputs of affected, other control units.
It is considered disadvantageous in this connection that the handling of inputs and outputs is complicated and error-prone. In addition, there are additional system engineering costs, because the physical inputs and outputs or the field bus system must firstly be made available. The control units to be synchronized must also be constructed in coinciding manner so that the particular inputs and outputs have the same significance, which restricts the possible uses of such methods. As the control units do not normally communicate with one another directly by means of a field bus, but instead by means of an interconnected stored programmable system control (system SPC) the latter must take account of a corresponding mapping of the inputs and outputs.
Thus, an extended communication between cooperating control units, apart from a modification to the control programs, also involves an adaptation of the input and output configuration, linked with additional lines in the case of physical inputs and outputs, additional programming costs for the SPC, etc. The synchronization points within the program, i.e. program points where there are synchronization instructions, must be clear and unambiguous, so that it is necessary in known synchronization methods to use an individual output for each synchronization point, because otherwise in the case of a set or record selection within the control program, i.e. a selection of specific program parts, which correspond to a specific geometrical position of the manipulator, the synchronization can take place at an incorrect geometrical position.
Methods for the synchronous control of cooperating robots are e.g. known from EP 1 186 386 A2 and EP 1 090 722 A2. The aforementioned documents disclose the synchronous working of a plurality of robots, which as a function of their instantaneous operation can be subdivided into master robots, slave robots and “normal”, i.e. independent robots. By means of communication lines there is an active exchange of position data and interpolation data (on-line calculated intermediate positions of movements with a high time density), which the master regularly transmits to all the slaves, so that on a higher hierarchic plane the control unit of the master robot performs a master control function for all participating robots.
The master-slave concept is more particularly considered to be disadvantageous, because in this way a robot or a control unit must participate in every synchronization, so that there is a restriction during practical use regarding the flexibility of such a synchronization concept. In this connection EP 1 090 722 A2 discloses a synchronous control unit for several robots and their controls, which as a function of the group formed (group in connection with a specific application of robots to be synchronized), can either be used as a master, a slave or group-independent. For this purpose several complete, independent program sequences are loaded or stored in each control unit (master program, slave program, normal program), whereof in each case one is processed depending on the group formed. Therefore the program sequences must be coordinated and fixed from the outset.
In addition, all the participating robots, i.e. masters and slaves, wait for one another following a specific number of synchronously performed interpolation steps before there is a further programming or movement. Thus, all the synchronous sequences are time-lengthened, because in certain circumstances some robots are prevented from performing additional operations in the meantime or all the robots must wait for the slowest.
Furtheron, the continuous transmission of position and interpolation data implemented in the prior art is complicated and fault-prone from the data-engineering standpoint. Whilst obviating the aforementioned disadvantages, the problem of the invention is to provide a flexible method and an apparatus suitable for the performance thereof for the synchronous control of manipulators, accompanied by the simplification of communications between two or more control units, whilst ensuring a reliable reaction of the control program in the case of set selection. The invention is based on the further problem of making synchronization processes more reliable from the control engineering standpoint and of shorter duration.